Field of the Invention
The present invention relates to a lithography apparatus, a lithography method, and an article manufacturing method.
Description of the Related Art
Along with miniaturization or complication of a circuit pattern, an exposure apparatus for manufacturing a semiconductor device is required to have a technique of accurately exposing an electronic circuit pattern formed on an original (reticle) to light with respect to patterns on a substrate (wafer) in a superimposed manner. Therefore, a technique of accurately measuring an array that has already been patterned on the wafer (alignment measurement) and precisely performing exposure in accordance with its grating or shot shape is important.
An alignment measurement method includes global alignment (a method of predicting an overall array tendency by measuring representative sample shots) and die-by-die alignment (a method of measuring all shots and directly measuring the position of each shot). Global alignment predicts the array tendency of the entire shot by measuring the positions of the representative sample shots and obtains the position of each shot. On the other hand, die-by-die alignment directly measures the position of each shot by observing an original-side mark and a wafer-side mark for each shot. An alignment measurement method to be adopted is determined in accordance with required alignment accuracy or a processing time allowed for an exposure process. A wafer needs to be conveyed from a conveying unit to a stage in order to perform alignment measurement of a pattern on the wafer. When transferring the wafer, a rotation position at the time of transferring the wafer is determined by various methods such as position detection of the notch or the orientation flat of the wafer, or positioning of the outer shape of the wafer.
However, accuracy in determining the rotation position with respect to the stage of the wafer includes at least an error caused by measurement and a transfer error derived from stage accuracy. Even if the wafer can be transferred onto the stage correctly without any rotation positional shift, patterning having a rotation error may have originally been performed on the wafer. It is therefore necessary, when mounting the wafer onto the stage, to perform alignment measurement accurately (at a high magnification) to check the magnitude of a rotation error of the pattern on the wafer with respect to the orthogonal coordinate system of the stage. When performing alignment measurement at a high magnification, rough (low-magnification) measurement is performed in advance to grasp the magnitude of the rotation error of the pattern on the wafer with respect to the orthogonal coordinate system of the stage so as to place a mark in the field of a high-magnification scope. With low-magnification measurement, the rotation shift amount of the pattern is grasped, the stage is rotated by that rotation shift amount, and then alignment measurement is performed at a high magnification.
After low-magnification measurement, when the stage is rotated based on that measurement result, the positional relationship between a bar mirror and an interferometer of the stage changes, and the verticality between the bar mirror and the optical axis of inspection light of the interferometer is deteriorated, causing an Abbe error in high-magnification aliment measurement. This Abbe error may have an influence on the high-magnification alignment measurement result, decreasing overlay accuracy. In order to prevent the decrease in overlay accuracy caused by the Abbe error, Japanese Patent Laid-Open No. 9-260274 and Japanese Patent No. 4449457 each disclose a method of measuring an Abbe error and correcting, with that measurement result, a high-magnification alignment measurement result.
When using the exposure apparatus, the position of the stage which measures marks formed on the wafer by an alignment scope and the position of the stage when exposing the aligned wafer to light via a projection optical system are different. Therefore, when using the stage which controls the position by the interferometer, an encoder, or the like, an influence on positioning accuracy caused by the Abbe error differs between the times of alignment measurement and exposure due to the distortion of the bar mirror itself or the mounting error of the optical system. When mounting the wafer onto the stage, the rotation and the tilt error of the wafer differ for each wafer and for each lot due to position detection of the notch or the orientation flat of the wafer, the positioning error of the outer shape of the wafer, the difference from another exposure apparatus, film thickness unevenness in a process, or the like. Therefore, the positioning error of each wafer is increased in accordance with the rotation position and the tilt orientation of the stage, and is readily influenced (changes).
Therefore, even with the method of correcting the position measurement result of the stage with the measurement result of the Abbe error as in a prior art, the position measurement result itself has an error when, for example, the mounting state of the bar mirror, the interferometer, or the encoder changes in accordance with an elapse time or heat. Not only the exposure apparatus but also another lithography apparatus such as an imprint apparatus or a charged particle beam drawing apparatus has such a problem of the positioning errors of the wafer.